It is customary to provide mechanical stops at the ends of the guide which is normally disposed at one side of a scraper-chain conveyor disposed along the working and alongside the mineral face. It is also known from DE-3017756 to arrange limit switches near the ends of the guide which are actuated by the passage of the machine and cause one or both drive assemblies at the ends of the working to slow the machine to a creeping speed as it approaches one of the end stops. Once the machine has passed one of the limit switches its subsequent passage depends on a number of factors primarily the speed of the machine when it reaches the limit switch and the consequential inertia of the machine, the frictional forces in the drive to the chain and acting on the chain as well as the frictional forces between the guide and the machine and between the cutting implements of the machine and the mineral face and the extent to which any accumulations of material impede the movement of the machine.
A control system is known from "Bergbau" April 1976 page 111-114 in which a transmitter is provided on the body of a plough which provides signals detected by receivers disposed at set locations along the path of movement of the plough. The received signals are then used to effect halting of the movement of the plough at the ends of its path of movement.
If a machine or plough is traveling at high speed towards one of the end stops there are considerable forces and stress placed on the drive and the chain when the machine is slowed down and this can cause permanent deformation of the chain. In modern high performance mineral mining installations it is common to use an overload protection means which disengages the drive to the haulage chain usually through a clutch in the event of abnormally high forces. When the machine is being slowed down the clutch is apt to slip and this produces high wear. These problems are frequently aggravated when the machine is operating over regions of the mineral face which are difficult to mine effectively. Examples of an overload protection means which utilizes a rapidly responding electromagnetic valve to actuate the clutch in the event of an overload condition are described in "Gluckauf" 1990, page 621-627. U.S. Pat. No. 4,667,790 and DE-3 720 208 the contents of which are herein incorporated by reference.
Hitherto it has not proved possible to control the movement of a machine or plough efficiently at the end regions of its path of movement.
A general object of the present invention is to provide an improved control system which can control the showing and halting of a machine or plough in a reliable and optimal fashion even when the machine is moving at high speed and which ensures there are no harmful effects due to the high forces which have to be dissipated.